A study of the radiative transition π π \to π γ^{\ast} with lattice QCD
Abstract
Lattice QCD calculations of radiative transitions between hadrons have in the past been limited to processes of hadrons stable under the strong interaction. Recently developed methods for $1\to2$ transition matrix elements in a finite volume now enable the determination of radiative decay rates of strongly unstable particles. Our lattice QCD study focuses on the process $\pi \pi \to \pi \gamma^{*}$, where the $\rho$ meson is present as an enhancement in the crosssection. We use $2+1$ flavors of clover fermions at a pion mass of approximately $320$ MeV and a lattice size of approximately $3.6$ fm. The required $2$point and $3$point correlation functions are constructed from a set of forward, sequential and stochastic light quark propagators. In addition to determining the $\rho$ meson resonance parameters via the Lüscher method, the scattering phase shift is used in conjunction with the $1\to2$ transition matrix element formalism of Briceño, Hansen and WalkerLoud to compute the $\pi\pi\to\pi\gamma^{*}$ amplitude at several values of the momentum transfer and $\pi\pi$ invariant mass.
 Publication:

Proceedings of the 34th annual International Symposium on Lattice Field Theory (LATTICE2016). 2430 July 2016. University of Southampton
 Pub Date:
 2016
 arXiv:
 arXiv:1611.00282
 Bibcode:
 2016slft.confE.159L
 Keywords:

 High Energy Physics  Lattice
 EPrint:
 7 pages, 4 figures, presented at the 34th International Symposium on Lattice Field Theory (Lattice 2016), 2430 July 2016, Southampton, UK